It is known that a television camera can be disposed in the beam path of a motion picture camera making it possible to view on a screen or record on a video recorder the frame independently of the optical finder mounted on the motion picture camera. This also makes it possible to view the frame at a point remote from the motion picture camera and to evaluate the frame immediately without time-consuming development of the motion picture film. The television camera is located in the vicinity of the optical finder of the motion picture camera, i.e. in the beam path behind the rotating mirror shutter, with a beam splitter sending one part of the light reflected by the rotating mirror shutter into the optical finder and another part to the lens of the television camera.
Since the image received by the television camera depends on the taking speed of the motion picture camera and hence on the rotational speed of the rotating shutter of the camera, at certain taking speeds a highly disturbing flickering of the brightness in the video image occurs. Therefore when a television camera is adapted to a motion picture camera it is necessary when evaluating the video image generated by the television camera to eliminate the highly disturbing flickering in the video image that results from using the light reflected from the motion picture camera mirror shutter with a mirror sector which is generally 180.degree..
Without suitable additional electronics, when using a tube camera as a television camera and a rotational frequency of the mirror shutter as well as a video image frequency of 25 Hz for example, a flickering brightness would result in the video image with a node and antinode in the vertical. At different rotational frequencies of the mirror shutter, on the other hand, the antinode and node, depending on the difference between the rotational frequency of the mirror shutter and the video image frequency, move upward or downward constantly through the video image. Image modulation increases sharply as the rotational speed of the mirror shutter decreases.
FIG. 1 is a block diagram explaining the principle of a television recording from a tube camera 1 coupled with a motion picture camera. Motion picture camera 2 has a lens 21, a rotating mirror shutter 22, and a film plane 25 in which the motion picture film is moved. The light reflected from rotating mirror shutter 22 passes through a ground glass 24 and a beam splitter 26, from which a portion of the beams is conducted to optical finder 27 of motion picture camera 2 and a portion through a camera connection 28 to television camera 1.
The output of television camera 1 is connected by an analog-digital converter 3 and an electronic switch 40 with two video field memories 41, 42, whose output is likewise connected through an electronic switch 43 with a digital-analog converter 6. Two video fields make up one video image.
A sensor 23 provided in motion picture camera 2 detects the rotational speed and position or phase of rotating mirror shutter 22 and delivers a corresponding signal to a control electronic circuit 5, which controls both television camera 1 and video field memories 41, 42 as well as electronic switches 40, 43 and digital-analog converter 6. The output of digital-analog converter 6 is normally connected to a screen 7 and/or a video recorder 8.
The coupling of motion picture camera 2, television camera 1, and the two video field memories 41, 42 makes it possible to eliminate the flickering in the brightness of a tube camera by controlling the scanning of the taking tube of television camera 1 by the position and rotational speed signal of mirror shutter 22 output in sensor 23. With each revolution of mirror shutter 22, exactly one video video field is scanned and recorded in one of the two video field memories 41 and 42. This video field memory 41 or 42 is then repeatedly read until a new video field is stored in the other field memory 42 or 41.
In contrast to television cameras with image tubes, television cameras with semiconductor sensors have the advantage that the television camera need not be re-equipped for the special application of coupling with a motion picture camera or developed for such operation. In addition, television cameras with semiconductor sensors are operated asynchronously and may be synchronized with other television signals as well.
Another important advantage consists in the fact that no image memory is required, with costly control electronics and no analog/digital or digital/analog converter.
Finally, the detail resolution in the vertical of a television camera with semiconductor sensors corresponds to the motion picture camera and the television standard, while this is reduced by half in the vertical in a tube camera with a memory system, since the video fields to be stored are always identical.
Given the advantages of a television camera with semiconductor sensors, the only disadvantage is that in a tube camera with a memory system a video image can be "frozen" and displayed mixed with the current signal with the motion picture camera not running.